WASHINGTON — House Democrats formally launched their bid Monday to further slash defense spending and rechannel the money to domestic programs, vowing to cut the Pentagon's budget another 33% to 40% over the next decade and earmark $400 billion for domestic spending.

At the request of the House leadership, Rep. Leon E. Panetta (D-Carmel Valley), the House Budget Committee chairman, outlined a sweeping plan that would mandate massive spending for education, health care and economic growth while providing tax relief for the middle class.

The move by the Democrats is expected to start unraveling last autumn's budget accord between Congress and the White House and pave the way for a free-for-all in Congress on the budget issue, which Democrats see as a potential major battleground in the 1992 election campaign.

The rush to cut defense spending has intensified following Bush's proposal to eliminate tactical nuclear weapons and Soviet President Mikhail S. Gorbachev's response, offering to scale back his country's nuclear arsenal.

Panetta said he will invite congressional Republicans to join Democrats this week in closed-door sessions aimed at reshaping the budget accord, and GOP leaders said they would participate--though they declined to commit themselves to altering the 1990 pact.

The White House, which wants domestic spending held in check, continued to be cautious. "We do not want to . . . reopen the budget agreement," said White House spokesman Marlin Fitzwater. "We don't expect it to be reopened and certainly have no plans to do that."

The plan unveiled by Panetta calls for slashing defense spending by "up to $600 billion" between now and the year 2001, amounting to a 40% cut in the Pentagon budget--compared to a 25% cut in the current budget accord.

The bulk of the savings over 10 years, a total of some $1 trillion, would be earmarked to reduce the federal deficit.

But the Democratic plan would rechannel almost $400 billion to "investment" in federal education programs, health care and "economic growth," which Panetta called "three areas critical to our future."

Ironically, the education goals outlined by Panetta are virtually identical to those in the Bush Administration's own education plan--upgrading science and math, improving literacy, cutting the high school dropout rate and expanding preschool training to children who need it.

Unlike the Administration's proposals, however, the Democrats' education plan calls for massive new federal spending of between $100 billion and $120 billion over the decade, Panetta said.

On the health care issue, the Democratic program calls for "a self-financing nationwide program that guarantees affordable health coverage for every American," reducing infant mortality by 50% and intensifying research to cure cancer, heart disease and AIDS.

Panetta gave no details, but he estimated that the health care component of the plan would require federal expenditures of an additional $75 billion to $90 billion over the decade.

The economic growth package outlined by Panetta includes tightening environmental controls and reducing energy consumption by 15% by the end of the decade; massive federal spending for housing, roads, bridges and mass transit and an expanded job-training program.

It also would offer tax relief for the middle class, to be offset in part by higher taxes on the rich.